Need advice..Are these hot pixels?

[gollum]

are the dots on the sky hot pixels?

Long Exposure on D90 on 35mm F2

[krion]

Do you have a filter on your lens?

[gollum]

Originally Posted by krion Do you have a filter on your lens?

yeah using hoya uv

happens for long exposures only though

[MrJelly]

stars at night? or a group of UFOs flying around? well, I dont no

[Sleepwalker]

Hoya? It seems it needs to be replaced for something better or taken of for such shots. On photo 2 structure you can see on the sky is inverted picture of the crane and lights line below. So don't worry, not hots nor alien invasion :-)

[viix]

If you want to test for hot pixels, aim at something pitch black..
Anyway these ain't hot pixels.. they are usaully Red green or blue with no Halo~

[flowerpot]

my best guess its the stars lah... their position with reference to the building is always the same... i always get these spots until i realize they are always at the same position with reference to the buildings

[lsisaxon]

Originally Posted by flowerpot my best guess its the stars lah... their position with reference to the building is always the same... i always get these spots until i realize they are always at the same position with reference to the buildings

Those spots are reflections from the bright light sources in the picture. They are exactly the inversion of the bright light sources. So go work the rest of them out yourselves. These light sources must be directly shining into the lens to give you this kind of reflections. It will be worse if you're using a cheap non-multicoated filter. Even without filter, you may sometimes get this kind of reflection from the internal reflections from the optical elements.

The best multicoating doesn't eliminate the reflections. It may cut down reflections to only about, say, 1% but there is still some contribution, 1% is roughly about 7 stops down. Considering that it only happens in long exposure, the original light sources are blown by don't know how many stops already.

[gollum]

wah reflections ah..

any idea did the problem come from the filter or the lens?


edit : nvm i test again soon and post results

[lsisaxon]

Originally Posted by gollum wah reflections ah.. any idea did the problem come from the filter or the lens? edit : nvm i test again soon and post results

If you remove the filter and no more reflections, then it's from the filter loh.. Otherwise there is nothing else left for you to remove already..

[gollum]

Originally Posted by lsisaxon If you remove the filter and no more reflections, then it's from the filter loh.. Otherwise there is nothing else left for you to remove already..

heh got ah...self given excuse to change some glass

[lsisaxon]

Originally Posted by gollum heh got ah...self given excuse to change some glass

But let's be practical, the ultimate best in multicoating I've encountered is able to give a transmission about 99.8% which means which means that 0.2% is lost in reflection or absorption. Let's assume that half is reflected and half is absorbed, the reflection would be 0.1%. That's about 10 stops. So if the background is more than 10 stops darker than the light source, chances is that the background is not able to cover up the reflections from the light sources.

In situations like these, I think might be easier/cheaper to clone away the spots.

[gollum]

Originally Posted by lsisaxon But let's be practical, the ultimate best in multicoating I've encountered is able to give a transmission about 99.8% which means which means that 0.2% is lost in reflection or absorption. Let's assume that half is reflected and half is absorbed, the reflection would be 0.1%. That's about 10 stops. So if the background is more than 10 stops darker than the light source, chances is that the background is not able to cover up the reflections from the light sources. In situations like these, I think might be easier/cheaper to clone away the spots.

yea...true..so might be better to increase iso reduce exposure at the end of the day..


was doing very long exposures some where further back there was intense lightning storm..capturing lightning and saw these.

[lsisaxon]

Originally Posted by gollum yea...true..so might be better to increase iso reduce exposure at the end of the day.. was doing very long exposures some where further back there was intense lightning storm..capturing lightning and saw these.

Eh.. I think reduce exposure and increasing ISO would not help.. It's basically the contrast between the lights and the sky. So one way is to get them to dim down the lights or get the skies to brighten up a bit.. Nothing much you can do at your side..

[sneakyho]

Originally Posted by gollum [IMG] are the dots on the sky hot pixels? Long Exposure on D90 on 35mm F2

You can check out this site for a program that can help to spot hot or dead pixel. Tested on mine but detected no issue. Check this out if it works for you.

http://www.starzen.com/imaging/deadpixeltest.htm

[kkcharles82]

Multiple reflections is exactly why I never use the front filter protection for any of my lenses. Unless you use some fairly expensive B+W filter, chances are that if you shoot at night, you are going to get multiple reflections.

[gollum]

Did some again without the filter and no spots at all even at 30 secs exposure.

[MSZ006Zeta]

It's your filter alright. When you're shooting at night, it's advisable to remove your filter. You don't want any flair or reflections in your pictures.

[lsisaxon]

Originally Posted by gollum Did some again without the filter and no spots at all even at 30 secs exposure.

So now you know..

[gollum]

Originally Posted by lsisaxon So now you know..

tks for the info